The present invention relates to a means of bonding a coating material to an article and more particularly to means of bonding a uniform coating material to an article in which metallurgical properties of the substrate material of the article are carefully controlled in the process.
It has been found advantageous to coat a substrate with a coating having special properties, for example, wear resistance or corrosion resistance. A method for providing this coating on a substrate is the use of flexible preforms using fibrillated polytetrafluoroethylene (PTFE) as the binder material as disclosed in U.S. Pat. No. 3,743,556. The method for metallurgically bonding the flexible preform containing the coating material onto the substrate material has been furnace fusion, either a forced atmosphere furnace using a protective atmosphere, or a vacuum furnace. A major limitation to this approach, however, is the necessity to expose the entire substrate to the required high fusion temperature. This can have an undesirable effect on the substrate material by promoting metallurgical changes such as grain growth or phase changes that could significantly influence the performance characteristics of the substrate. Further, the propensity for article distortion is high. Still another limitation of the conventional use of furnace fusion is the article size that can be accommodated in the furnace and the economics of the energy use associated with furnace heating and atmosphere control, especially when only a small area has to be coated on a relatively large article.
Some of the above-mentioned limitations can be partially overcome with the use of resistance fusion techniques, as disclosed in U.S. Pat. No. 3,778,586. However, this resistance fusion technique has the limitation that the coating area has to be quite small.
Accordingly, it is a principal object of this invention to provide a means for applying a uniform coating material to an article in which the heating of the substrate material of the article to produce the bond is needed to be selectively controlled.
Another object of this invention is to provide a means for applying a uniform coating material to an article in a continuous manner and/or having a large or irregular surface area.
Other objects of the invention will become apparent to those skilled in the art from a reading of the following specification and claims.